Controls of mantle potential temperature and lithospheric thickness on magmatism in the North Atlantic Igneous Province.

Modelled primary magma compositions of Palaeocene basalts from the North Atlantic Igneous Province (NAIP) require melting at mantle potential temperatures (TP) in the range 1480-1550°C. Modern lavas from the Icelandic rift-zones required TP~1500°C and those from the rift-flanks TP~1450°C. Secular cooling of the NAIP thermal anomaly was therefore in the order of ~50°C in 61 Ma. There were systematic variations in TP of 50-100°C from centre of the thermal anomaly to its margins at any one time, although limits on the stratigraphical distribution of TP determinations do not rule out thermal pulsing on a timescale of millions of years. Variation in extent of melting at similar TP was controlled by local variability in lithospheric thickness. In the west of the NAIP, lithosphere varied from ~90 km at Disko Island to ~ 65 km at Baffin Island, with similar thickness variations being evident for magmatism in the Faroe Islands, Faroe-Shetland Basin and the British Palaeogene Igneous Province (BPIP). Mean pressure of melting ≥ final pressure of melting and the two values converge for melting columns with a melting interval of < 1.5 GPa, regardless of TP. In particular, the majority of BPIP magmas were mostly generated in the garnet-spinel transition in the upper-mantle. Calculated and observed rare earth element distributions in NAIP lavas are entirely consistent with the melting regimes derived from major element melting models. This allows a calibration of rare earth element fractionation and melting conditions that can be applied to other flood basalt provinces.